The present invention relates to a scroll type fluid machine and, more particularly, to a scroll type fluid wherein an abnormal pressure rise in the suction chamber which may occur when the machine is reversed is avoided.
A scroll type fluid machine has a compressor section and an electric motor section mounted in a hermetic container, with fluid passages being formed to extend through the walls of the hermetic container and be connected through pipes to external equipments such as, for example, an evaporator and condenser, when the machine is used in a refrigeration system.
The scroll type compressor section has a compressor which is constituted by a stationary scroll member and an orbiting scroll member mated therewith. These scroll members have spiral wraps formed in conformity with an involute curve or a curve approximating involute curve so as to protrude upright from the end plates. These scroll members are assembled together such that their wraps mesh each other to form therebetween compression chambers the volumes of which are progressively changed in accordance with an orbital movement of the orbiting scroll member. A fluid suction port is communicated with a portion of the stationary scroll member near the radially outer end of the outermost compression chamber, while a fluid discharge port opens in the portion of the stationary scroll member close to the center thereof. An Oldham's ring mechanism is placed between the orbiting scroll member and the frame or between the orbiting scroll member and the stationary scroll member, so as to prevent the orbiting scroll member from rotating about its own axis. The orbiting scroll member is driven by a crankshaft connected thereto so as to make an orbital movement with respect to the stationary scroll member without rotating about its own axis. Consequently, the volumes of the compression chambers mentioned before are progressively decreased to compress the fluid confind in these chambers, and the compressed fluid is discharged from the discharge port as the compression chambers are brought into communication with the discharge port. In order to attain a high compression efficiency in the operation of the scroll-type compressor, therefore, it is quite essential that the orbiting scroll member is pressed to the stationary scroll member at a moderate pressure.
The force for pressing the orbiting scroll member onto the stationary scroll member is derived as the difference between the force produced by the pressure acting on the rear side of the orbiting scroll member and the force produced by the fluid which is being compressed and thus acting on the front or inner side of the orbiting scroll member. The force acting on the rear side of the orbiting scroll member is produced by the fluid pressure which is transmitted from the compression chambers to a back pressure chamber formed on the rear side of the orbiting scroll member, through a small passage bore or bores.
The lubrication of the bearings and sliding parts of the machine including the meshing parts in the compressor section is achieved by a lubricating oil which is drawn up from a well or reservoir formed in the hermetic container. More specifically, the lubricating oil is drawn up through an oil passage bore formed in the crankshaft, is supplied to the bearings by the pressure difference between the intermediate pressure and the high pressure attainable in the compressor, and is then introduced into the back pressure chamber behind the orbiting scroll member. The lubricating oil supplied to the back pressure chamber is discharged into the compression chambers at a moderate rate through the small passage bore and is circulated together with the compressed gas. This scroll-type compressor is shown, for example, in Japanese Patent Laid-open No. 73886/1982.
In order to prevent any reversing of the fluid from the high-pressure side to the low-pressure side during the suspension of operation of the compressor, a discharge valve, disposed in the high-pressure gas discharging passage of the compressor, is adapted to be closed when the compressor stops so that the pressures in the compression chambers are balanced with the low pressure of the suction side. Meanwhile, the lubricating oil also flows out undesirably to the suction side through the passage bore by the pressure difference. Consequently, the amount of the lubricating oil held in the oil well or reservoir in the hermetic container is decreased to such an extent that there is a failure in the supply of the lubricating oil at the time of re-starting of the compressor so as inadequate and to causes troubles such as burning of the bearings and other sliding portions requiring lubrication.
If the discharge valve mentioned before is neglected, the compression chambers are filled with high-pressure gas after stopping of the operation of the compressor, so that the escape of the lubricating oil to the suction side is avoided. In this case, however, the orbiting scroll member is reversed by the difference of the pressure between the discharge side and the suction side, generating a large level of noise.
In the scroll type compressor in which the lubricating oil is supplied by the differential pressure established in a refrigeration cycle, therefore, it is necessary to prevent both the reversing of the orbiting scroll member due to reversing flow of the pressurized fluid and escaping of the lubricating oil to the low-pressure side, during the suspension of operation of the compressor.
In view of the above, it has been proposed to provide a scroll type compressor provided with a check valve disposed in the suction passage leading through the end plate of the stationary scroll member, as disclosed in the specification of U.S. Ser. No. 559,089 entitled "SCROLL-TYPE COMPRESSOR".
It is, however, necessary to further consider a measure for a phenomenon of establishment of local abnormal high pressure in the compression chambers which is accidentally encountered by the above scroll-type machine due to the presence of the suction check valve, otherwise the wrap wall of the orbiting scroll member would be excessively loaded to cause a chance of breakdown of a part of the wrap wall. This phenomenon is serious particularly when the gas has a large liquid content including the liquefied phase of the working fluid and the lubricating oil.